1. Field of the Invention
The present invention relates to a golf ball-shaping mold and cavity die to be used to manufacture a golf ball. More particularly, the present invention relates to improvement of a flow path for flowing a temperature-adjusting fluid therethrough.
2. Description of the Related Art
In the molding process of a golf ball such as a two-piece golf ball, a multi-piece golf ball, and a thread-wound golf ball, its core is covered with a cover. As the method of covering the core, injection molding method or compression molding method is adopted. In both molding methods, a pair of upper and lower cavity dies is used. Each cavity die has a semispherical cavity surface. Thus, the two cavity surfaces form a spherical cavity. In the injection molding method, a heated/melted material (normally, thermoplastic resin) of the material of the cover is injected on the peripheral surface of the core, with the core held in the cavity. In the compression molding method, the core and the material of the cover are introduced into the cavity to heat and compress them. The one-piece golf ball that is mainly supplied to a golf practice range does not have the cover but consists of solid rubber. A pair of upper and lower cavity dies is also used to shape the one-piece golf ball. In the case of the one-piece golf ball, a rubber material is introduced into the cavity and heated and compressed (compression molding).
To obtain high-quality golf balls in these molding methods, temperature adjustment of the cavity die is important. The temperature control can be achieved by a heating medium flowing through a flow path formed in a mold including a cavity die. For example, the temperature of the cavity die is raised by a heated heating medium flowing through the flow path, whereas the temperature of the cavity die is lowered by a cooled heating medium flowing therethrough. Water (hot water) is generally used as the heating medium.
In the injection molding method, the temperature of the cavity die becomes high because high-temperature thermoplastic resin is injected thereinto. Thus, cooling the cavity die is important. When the cavity die has a high temperature, the injected thermoplastic resin (cover) is not cooled sufficiently. In this case, when the shaped golf ball is ejected from the cavity with an ejection pin, the soft cover is damaged with the tip of the ejection pin to generate a so-called pin mark. The generation of the pin mark can be prevented by cooling the golf ball for a long time, which makes a golf ball-shaping cycle long and deteriorates productivity.
FIG. 5 is a sectional view showing a conventional golf ball-shaping mold. The mold has a cavity die 101 and a retaining plate 103 in which the cavity die 101 is fitted. Heating medium flow paths 105 are formed in the retaining plate 103. In this mold, there is a long distance between the flow path 105 and a cavity surface 107. Thus, heat exchange cannot be made sufficiently, and hence the temperature adjustment of the cavity die cannot be sufficiently made.
FIG. 6 is a sectional view showing another conventional golf ball-shaping mold. The mold has a cavity die 109 and a retaining plate 111 in which the cavity die 109 is fitted. An annular groove 115 is formed on the periphery of a body 113 of the cavity die 109. The portion surrounded with the annular groove 115 and the retaining plate 111 serves as a flow path 117. In the mold, the side portion of a cavity surface 119 is near to the flow path 117. Thus the temperature adjustment of the side portion is efficiently accomplished, whereas the neighborhood of the bottom portion of the cavity surface 119 is far from the flow path 117 and thus the temperature adjustment thereof is not efficiently accomplished. If the mold is used as the injection molding mold, an ejection pin is formed near the bottom portion of the cavity surface 119. Therefore, when the neighborhood of the bottom portion of the cavity surface 119 is insufficiently cooled, the pin mark is liable to be generated.
A cavity die having an annular flow path formed in its body is disclosed in Japanese Patent Application Laid-Open No. 7-137038. Because in the cavity die, the distance (shortest distance) between the cavity surface and the flow path is short, heat exchange can be made efficiently.
The annular flow path cannot be machined with an ordinary cutting tool. Thus the manufacturing cost of the cavity die is high. As described above, the distance (shortest distance) between the cavity surface and the flowpath is short. Therefore, the temperature-adjusting efficiency in the portion of the cavity surface near the flow path maybe different from that in the portion thereof far from the flow path, which may lead to nonuniform temperature distribution of the cavity surface. To allow the temperature distribution thereof to be uniform, it is necessary to form a plurality of annular flow paths from an upper portion of the body of the cavity die to a lower portion thereof. But as described above, it is difficult (impossible with ordinary cutting tool) to machine the annular flow path. Therefore, forming a plurality of the annular flow paths leads to increase in the manufacturing cost of the cavity die.
The present invention has been made in view of the above-described situation. Thus, it is an object of the present invention to provide a golf ball-shaping mold or cavity die that has a high temperature-adjusting efficiency, prevents temperature distribution from becoming nonuniform, and can be easily manufactured.
To achieve the object, according to one aspect of the present invention, there is provided a golf ball-shaping mold comprising a cavity die having a body and a cavity surface; a retaining plate into which the cavity die is fitted; and a flow path, for flowing a temperature-adjusting fluid therethrough, formed inside the golf ball-shaping mold. The flow path includes an inner flow path formed inside the body of the cavity die and a boundary flow path located in a boundary between the cavity die and the retaining plate.
Thus, the flow path of the mold includes the inner flow path and the boundary flow path. As heat exchange is made by both the inner flow path and the boundary flow path, the temperature adjustment of the cavity die can be accomplished favorably without using a large number of inner flow paths. Therefore, the mold can be manufactured at a low cost.
Preferably, the inner flow path is approximately linear, and both ends of the inner flow path are formed as openings on a peripheral surface of the body of the cavity die. The inner flow path can be easily formed with a cutting tool or the like.
Preferably, the inner flow path is approximately linear, and one end of the inner flow path is formed as an opening on a peripheral surface of the body of the cavity die and the other end thereof is located inside the body of the cavity die such that the inner flow path communicates with another inner flow path at the other end thereof and inclines from the other end thereof to the one end thereof along the cavity surface. The inner flow path can be easily formed with a cutting tool or the like. Further, because the inner flow path inclines along the cavity surface, it can contribute to uniformalization of temperature distribution of the cavity surface.
Supposing that a distance between the inner flow path and the cavity surface is t and that a distance between the boundary flow path and the cavity surface is T, the ratio t/T is preferably not less than 0.5 and not more than 1.5. Thereby, heat exchange can be accomplished almost equivalently by the inner flow path and the boundary flow path.
Preferably, the t which is the distance between the inner flow path and the cavity surface is not less than 6 mm and not more than 12 mm; and the T which is the distance between the boundary flow path and the cavity surface is not less than 6 mm and not more than 12 mm. Thereby, it is possible to prevent the temperature distribution of the cavity surface from becoming nonuniform.
To achieve the object, according to another aspect of the present invention, there is provided a golf ball-shaping cavity die comprising a body; a cavity surface; and an approximately linear inner flow path, for flowing a temperature-adjusting fluid therethrough, formed inside the body. The inner flow path can be easily formed with a cutting tool or the like.